An overview of the learning notes of the triumphantly-Java EE (i)

j2ee| notes
Today, I began to learn the Java EE!

Goal: As far as possible in the shortest time, the Java EE architecture related to know about a, and then slowly to the depths of learning.

Come on! Come on!! Come on!!!
One, distributed multi-tier applications


Figure 1 Distributed multi-tier applications

The J2EE platform uses a multi-tier distributed application model. The application logic is divided into several components according to its function, and various application components form the Java-EE program distributed on the different layer-dependent machines. Components located at different levels are:

☆ client layer components running on the client

☆ the network layer running on the Java EE server

☆ the logical layer running on the Java EE server

☆ The Enterprise information layer running on an EIS server

Although the Java EE application can be composed of three or four layers, Java EE applications are usually composed of three layers because they are distributed in three different locations: client, server, and backend database server. The three-tier application model, which runs in this way, expands the two-tier model based on customer/service.

The conclusions that can be drawn from figure I:

1, Java-EE applications are usually composed of three layers: customer layer, middle tier, enterprise Information System layer (EIS);

2, the intranet does not pass through the Firewall client can access the EJB (Enterprise JavaBeans) container and the Web container directly, while the client outside the firewall accesses through the firewall, can only access the Web container directly, this part of customers can access the EJB container only through the Web container;

3. All customers can access the EIS only through the EJB container.

Java EE component

The J2EE application is composed of components. The Java EE specification defines some of the following components:

☆ is running on client applications and applet programs.

☆ the servlet&jsp component running on the server network.

☆ The Enterprise Logic component--EJB running on the server side.

Java Client

Web browser

Small program

Application Client

JavaBean Component Structure

Network components

Business logic Components

The enterprise bean can retrieve the data from the memory again, if necessary and process it, and then send it to the client program.

There are three kinds of EJB: Session bean, Entity bean, message-driven bean.

The session Bean represents a short session with the customer, and when the client finishes executing, the session bean and its data disappear. Compared to session beans, entity beans represent tables stored in the database, and potential service methods store the data if the client ends the program or the server shuts down.

Second, the Java container



The container (Container) is the interface between the components and the underlying specific platforms (such as databases) that support the functionality of the component. Before you run Web Components, enterprise beans, or Java EE application clients, you must assemble them into a Java EE application and deploy them to the container.



Figure 2 Java Server and container (Container)

Java EE Server (Java)

The Run-time Services section of the J2EE product. A Java EE server provides an EJB container (EJB Container) and a Web container (Web Container).

EJB container

Manage the operation of enterprise beans in Java EE applications. Enterprise beans and their containers run in the Java EE service.

Web container

Manage the JSP page and the servlet component running in the Java EE application. Web Components and containers are also running in the Java EE service.

Application client container (Application client Container)

Manage the running of application client components. The application client and its container run on the client.

Applet container (Applet container)

Manage the operation of applets. Consists of browsers and Java Plug-ins running on the client.